Licenses: Change WTFPL to MIT (part 1)

Part 1: All mods except default and xpanes.
Add license.txt files.
Add missing README.txt files.
Check and update copyright years for all contributors.
Improve text format and make more consistent.

mods/doors/README.txt

@@ -1,62 +1,60 @@
 Minetest Game mod: doors
 ========================
-version: 2.0
+See license.txt for license information.
 
-License of source code:
------------------------
-Copyright (C) 2012 PilzAdam
-modified by BlockMen (added sounds, glassdoors[glass, obsidian glass], trapdoor)
-Steel trapdoor added by sofar.
-Copyright (C) 2016 sofar@foo-projects.org
-Re-implemented most of the door algorithms, added meshes, UV wrapped texture
+Authors of source code
+----------------------
+Originally by PilzAdam (MIT)
+
+Modified by BlockMen (MIT): Added sounds, glass doors (glass, obsidian glass) and trapdoor.
+
+Modified by sofar (sofar@foo-projects.org) (MIT):
+Added Steel trapdoor.
+Re-implemented most of the door algorithms, added meshes, UV wrapped texture.
 Added doors API to facilitate coding mods accessing and operating doors.
-Added Fence Gate model, code, and sounds
+Added Fence Gate model, code, and sounds.
 
-This program is free software. It comes without any warranty, to
-the extent permitted by applicable law. You can redistribute it
-and/or modify it under the terms of the Do What The Fuck You Want
-To Public License, Version 2, as published by Sam Hocevar. See
-http://sam.zoy.org/wtfpl/COPYING for more details.
 
-License of textures
---------------------------------------
-following Textures created by Fernando Zapata (CC BY-SA 3.0):
+Authors of media (textures)
+---------------------------
+Following textures created by Fernando Zapata (CC BY-SA 3.0):
   door_wood.png
   door_wood_a.png
   door_wood_a_r.png
   door_wood_b.png
   door_wood_b_r.png
 
-following Textures created by BlockMen (WTFPL):
+Following textures created by BlockMen (MIT):
   door_trapdoor.png
   door_obsidian_glass_side.png
 
-following textures created by celeron55 (CC BY-SA 3.0):
+Following textures created by celeron55 (CC BY-SA 3.0):
   door_glass_a.png
   door_glass_b.png
 
-following Textures created by PenguinDad (CC BY-SA 4.0):
+Following textures created by PenguinDad (CC BY-SA 4.0):
   door_glass.png
   door_obsidian_glass.png
 
-following textures created by sofar (CC-BY-SA-3.0)
+Following textures created by sofar (CC-BY-SA-3.0):
   doors_trapdoor_steel.png
   doors_trapdoor_steel_side.png
   door_trapdoor_side.png
 
-
-Obsidian door textures by red-001 based on textures by Pilzadam and BlockMen: WTFPL
+Obsidian door textures by red-001 based on textures by Pilzadam and BlockMen (MIT):
   door_obsidian_glass.png
 
-Glass door textures by red-001 based on textures by celeron55: CC BY-SA 3.0
+Glass door textures by red-001 based on textures by celeron55 (CC BY-SA 3.0):
   door_glass.png
-All other textures (created by PilzAdam): WTFPL
+
+All other textures (created by PilzAdam) (MIT):
 
 Door textures were converted to the new texture map by sofar, paramat and
 red-001, under the same license as the originals.
 
-Models:
---------------------------------------
+
+Authors of media (models)
+-------------------------
 Door 3d models by sofar (CC-BY-SA-3.0)
  - door_a.obj
  - door_b.obj
@@ -64,17 +62,18 @@ Fence gate models by sofar (CC-BY-SA-3.0)
  - fencegate_open.obj
  - fencegate_closed.obj
 
-License of sounds
---------------------------------------
+
+Authors of media (sounds)
+-------------------------
 Opening-Sound created by CGEffex (CC BY 3.0), modified by BlockMen
   door_open.ogg
 Closing-Sound created by bennstir (CC BY 3.0)
   door_close.ogg
 fencegate_open.ogg:
-  http://www.freesound.org/people/mhtaylor67/sounds/126041/ - CC0
+  http://www.freesound.org/people/mhtaylor67/sounds/126041/ - (CC0 1.0)
 fencegate_close.ogg:
-  http://www.freesound.org/people/BarkersPinhead/sounds/274807/ - CC-BY-3.0
-  http://www.freesound.org/people/rivernile7/sounds/249573/ - CC-BY-3.0
+  http://www.freesound.org/people/BarkersPinhead/sounds/274807/ - (CC-BY-3.0)
+  http://www.freesound.org/people/rivernile7/sounds/249573/ - (CC-BY-3.0)
 Steel door sounds open & close (CC-BY-3.0) by HazMatt
   - http://www.freesound.org/people/HazMattt/sounds/187283/
   doors_steel_door_open.ogg